Field of Disclosure
The following relates generally to wireless communication, and more specifically to superposition coding based preamble designs for co-existing radio access technologies (RATs), which in some examples may include the coexistence of a RAT employing Long Term Evolution (LTE) based protocols (e.g., LTE, LTE-Advanced (LTE-A), LTE-Unlicensed (LTE-U), etc.), and a RAT employing wireless local area network (e.g., Wi-Fi, etc.) protocols.
Description of Related Art
Wireless communication systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power). Examples of such multiple-access systems include code-division multiple access (CDMA) systems, time-division multiple access (TDMA) systems, frequency-division multiple access (FDMA) systems, single-carrier frequency-division multiple access (SC-FDMA) systems, and orthogonal frequency-division multiple access (OFDMA) systems.
By way of example, a first wireless multiple-access communication system may operate according to a first radio access technology (RAT), such as a wireless local area network (WLAN) technology, and may include a number of base stations or access points (APs), each simultaneously supporting communication for multiple mobile devices or stations (STAs). APs may communicate with STAs on downstream and upstream links. A second wireless multiple-access communications system may operate according to a second RAT, such as LTE, and may include a number of base stations, each simultaneously supporting communication for multiple communication devices, otherwise known as user equipments (UEs). A base station may communicate with UEs on downlink channels (e.g., for transmissions from a base station to a UE) and uplink channels (e.g., for transmissions from a UE to a base station). In some cases both types of communication systems may operate in the presence of one another (e.g., may be coexisting) and may both use shared resources of a radio frequency spectrum.
In a wireless local area network (WLAN), such as a Wi-Fi network, an AP may communicate with multiple STAs over a shared radio frequency spectrum band. The STAs may use contention procedures that include transmitting control frames prior to establishing a communication link, such that confirmation of the transmission via an exchange of control frames limits interference experienced by nearby communication devices. One example of such techniques include Request to Send (RTS) and Clear to Send (CTS) messaging, where, for example, an STA attempting to communicate with another device (e.g., another STA or AP), may first send an RTS frame to be received by the device. Once the recipient device receives the RTS frame, the recipient device may confirm the communication link by sending a CTS frame. After the CTS frame is received by the STA, the STA may then begin transmitting data to be received by the recipient device over the shared radio frequency spectrum band. In this way, RTS/CTS messaging can reduce frame collisions by enabling a device, such as a STA or AP, to clear and/or reserve at least a portion of the shared radio frequency spectrum band before transmitting data to an AP or STA.
In an LTE network, a base station and a UE may communicate over a dedicated frequency spectrum band or over different frequency spectrum bands of the radio frequency spectrum (e.g., a dedicated radio frequency spectrum band and a shared radio frequency spectrum band) of a cellular network. With increasing data traffic in cellular networks that use a dedicated (e.g., licensed) radio frequency spectrum band, offloading of at least some data traffic to a shared radio frequency spectrum band may provide a cellular operator with opportunities for enhanced data transmission capacity. A shared radio frequency spectrum band may also provide service in areas where access to a dedicated radio frequency spectrum band is unavailable. In some examples an LTE-U device over a shared radio frequency spectrum band may utilize an unlicensed radio frequency spectrum band, and may be referred to as an LTE-Unlicensed (LTE-U) device.
Prior to gaining access to, and communicating over a shared radio frequency spectrum band, a base station or UE may perform a listen before talk (LBT) procedure to contend for access to the shared radio frequency spectrum band. In some examples the LBT procedure may be compatible with contention procedures used by Wi-Fi devices to gain access to the shared radio frequency spectrum band. An LBT procedure may include performing a clear channel assessment (CCA) procedure to determine whether a channel of the shared radio frequency spectrum band is available. When it is determined that the channel of the shared radio frequency spectrum band is available, a channel usage beacon signal (CUBS) may be transmitted to reserve the channel. A different UE or base station may receive and decode the CUBS and discontinue contention procedures, while a STA or AP may monitor the channel and use energy detection to determine that a CUBS has been transmitted. After identifying the CUBS, other base stations or UEs may utilize resources on the shared radio frequency spectrum band that are not being used by the transmitting UE. After determining the detected energy is above a threshold, Wi-Fi devices may refrain from transmitting on the channel for a period of time. However, other Wi-Fi devices using resources of the channel may not determine that the energy of the CUBS does not exceed a threshold, or may not receive the CUBS at all. These other Wi-Fi devices may thus continue using the channel, or one or more interfering channels (e.g., an overlapping or adjacent channel), in a manner that interferes with the base station's or UE's reservation and use of the channel.
In some examples, a base station or UE may provide communications which rely on the increased sensitivity of a Wi-Fi device's signal reception and decoding circuit over the Wi-Fi device's energy detection circuit. In some examples, the energy detection circuit of a Wi-Fi device may be less sensitive than the signal reception and decoding circuit used for detecting Wi-Fi transmissions (e.g., Wi-Fi preambles, CTS-to-Self packets, Wi-Fi data packets, etc.). The base station or UE may thus transmit a channel reservation indication to be interpreted by the reception and decoding circuits of Wi-Fi devices. A channel reservation indication transmitted in this manner may be detected by the Wi-Fi devices in scenarios in which the energy level of a CUBS may not be detectable. However, if an LTE-U device transmits a Wi-Fi preamble, the other LTE-U devices within range may be unable to distinguish a Wi-Fi preamble sent from a Wi-Fi device from a channel reservation indicator sent from an LTE-U device. Therefore, an LTE-U device may not utilize the unused resources on the channel of the shared radio frequency spectrum band, resulting in an inefficient utilization of resources of the shared radio frequency spectrum band.